Mingzhi Li

Casing connection is a common connection method in oil and gas reservoir production, and the tripping of casing will seriously hinder the production process. To study the casing tripping process and the minimum tensile load required for casing tripping under different loosening buckle states, three kinds of casing tripping tensile tests were carried out. The thread morphology of the casing head and casing coupling was analyzed by local cutting at the end of the experiment, and the thread failure area was analyzed by scanning electron microscope, and then other loosening states were studied and analyzed using numerical simulation. The research results show that as the number of loosening buckles increases, the minimum tensile load required for the casing head and casing coupling to trip decreases. The observation of the thread shape shows that the thread part of the casing head was seriously damaged. Scanning electron microscopy results show that the fracture mode at the thread of the casing head is ductile fracture. Numerical simulation results show that the maximum stress area during the tripping process is at the contact position between the thread heads. Based on the experimental and numerical simulation results, the relationship between the number of casing loosening and the minimum tensile load required for casing tripping is obtained. The research results can be used as the experimental and theoretical basis for the investigation of casing tripping accidents and can also provide experimental reference for the design of the next-generation of casing.

Pipeline transportation has become the main mode of natural gas transportation. Due to inevitable aging, corrosion, and third-party damage, natural gas pipeline leakage accidents occur frequently. Leakage in the tunnel will lead to the leakage and accumulation of natural gas, and the potential explosion risk will threaten the tunnel's safety. It is significant to elaborate on the diffusion behavior of leaked natural gas in tunnel space for the traceability of leakage points and the formulation of safety technical measures. In this paper, a scale-down experimental platform for natural gas pipeline leakage in the tunnel is built, and the influence of pipeline pressure on natural gas diffusion characteristics is described. The results show that the diffusion process of leaked natural gas in the tunnel space shows obvious segmentation characteristics, and the concentration of natural gas reaches the maximum at the end of the continuous leakage stage. The increased pipeline pressure promotes natural gas diffusion, and the concentration of natural gas under 1.0 and 1.2 MPa rises sharply. First dangerous time (FDT) and maximum accumulated concentration (MAC) have a negative correlation with the leakage distance, while FDT and MAC have a good exponential and linear relationship with the pipeline pressure (0.2-1.2 MPa), respectively.

Frequent occurrence of indoor natural gas explosion accidents seriously threatens the safety of people and property. To determine the law of indoor natural gas leakage and explosion hazards, based on experiment and simulation, the nature of natural gas explosion, the distribution law of natural gas volume fraction, flame propagation, temperature, and shock wave overpressure were studied. The results show that the flame structure can be divided into three zones, i.e., preheat zone, reaction zone, and product zone. OH + CO ⇔ H + CO₂ is the main exothermic reaction in the combustion process. The overall distribution law of natural gas volume fraction shows that the higher the position, the greater the volume fraction, and the closer the distance to the leak source at the same height, the greater the volume fraction, and the natural gas volume fraction of the hose falling off is the largest under different leakage conditions. The difference in the wrapping structure of the kitchen package has a significant impact on the diffusion distribution of natural gas. The flame development goes through five stages of ignition, slow burning, detonation, slow burning, and extinguishing. The indoor temperature reaches about 1400 °C. Although the simulated value of shock wave overpressure is larger than the experimental value, the relationship between overpressure and distance is expressed by Y = A + B * ln(X + C). This study can provide certain technical support for natural gas accident rescue. The research can provide certain technical support for natural gas accident rescue and can also be used for accident investigation to form the determination procedure and method of leakage location and leakage amount.